Acid sulfate clean up has world wide implications

A dramatic improvement in environmental conditions has been achieved by researchers working on the Hills Creek catchment at the East Trinity site near Cairns, Queensland, using a combination of natural tidal action and strategic treatment with lime.
Mangrove and wetlands are returning, birdlife is flocking to the area and fish abound in creeks that once ran so acid, that nothing could survive in them. Having first demonstrated success in the trial catchment, remediation is underway on the remainder of the site.
The acid crisis at East Trinity began in the 1970s, when developers drained and cleared 800ha of tidal wetland mangroves to grow sugar. This dried out underlying acid sulfate soils, causing them to release slugs of acid whenever they were soaked by rain, leading to fish kills and loss of wetlands.
Today East Trinity is a world class demonstration of large-scale restoration in action, says CRC CARE MD Prof Ravi Naidu. “There are an estimated 40m ha of similar acid coastal wetlands round the world and at least 4m in Australia, including the lower Murray-Darling, and areas along the coasts of NSW, Qld, SA and WA,” he says.
The main restoration work, being carried out by the Queensland Department of Environment and Resource Management in partnership with CRC CARE and Southern Cross University, has made East Trinity a CRC CARE national demonstration site, providing a practical example of remediation in action. World leading, new scientific research, has been published by the team to assist with understanding the complex problem of remediating acid sulfate soils.
According to CRC CARE project leader Dr Richard Bush of Southern Cross University, restoration began in 2001 after the Queensland Government bought the land to remediate the acidic soils and protect the natural green backdrop to Cairns. The site was declared a ‘reserve for environmental purposes’.
“We decided to take advantage of the enclosing sea wall, built by the original developers, to exclude the tide and drain the site. We re-introduced a partial tidal exchange through adjustable floodgates, to gradually re-flood the most acidic sediments and prevent them producing more acid. Where the runoff was still too acid we added hydrated lime using specially designed equipment.”
Gradually mangroves began to recolonise, with a wider species diversity, than the scientists had dared hope.
“Birds are back too with more than 100 wild species observable within a 10 minute boat ride of the Cairns CBD. How many cities in the world can claim that?” Bush asked.
The once-sterile creeks, still stained in parts with the iron-red deposits from the acidification process, now swarm with tiny fish, creating an abundant nursery to rebuild fish numbers along the coast and nearby Great Barrier Reef.
“Essentially we are reversing the chemistry of what took place when the acidic soils were drained. If you tried to treat all the acid sulfate soil at East Trinity, according to current recommended practice, it would cost more than $300m and require complete vegetation clearing. Our process is returning nature for a mere fraction of that.”
To keep the acid at bay however, means that for a third of the site soils will have to remain permanently a tidal wetland, making it unsuited to major developments such as marinas or high-rise urban living. But Cairns could inherit a huge nature park with potential for an eco-tourist attraction right on its doorstep.
Besides developing a solution suitable for tidal wetlands almost anywhere, Naidu says the East Trinity approach could form the basis for a new export industry.
As communities see fish kills, dying estuaries and vanishing birdlife, the realisation is dawning that we have made some serious mistakes in how we developed these sensitive landscapes and people, are looking for answers, he said.
“The fact that Australia has devised and demonstrated a large-scale solution, creates a remarkable opportunity for a new form of knowledge exports. East Trinity is a global case study, and a beacon of hope that this can be achieved.”